1. Field of the Invention
The present invention pertains to a combination telescoping piston and cylinder suspension spring strut and vibration dampener for vehicle suspension systems.
2. Background
In the art of vehicle suspension systems there have been several developments directed to improving the isolation of the vehicle frame from stresses and excursions of the vehicle resulting from uneven or rough roadway conditions and other factors inducing vibration in the vehicle undercarriage. Hydraulic, and/or combination pneumatic and hydraulic suspension mechanisms are desirable for several reasons including improved fatigue life of the mechanism, improved vibration damping characteristics and the contribution of the mechanism to flexibility in the design of the vehicle undercarriage and frame. However, prior art hydraulic suspension spring and vibration dampener mechanisms have disadvantages which have presented certain problems to the art worker.
One problem associated with known types of liquid filled piston and cylinder type suspension mechanisms pertains to the build up of heat in the cylinder fuid as a result of inadequate dissipation of heat from the fluid volume contained within the cylinder. In all known liquid filled suspension mechanisms a moderate increase in temperature of the working fluid will cause thermal expansion resulting in changes in the ride height of the vehicle frame. Sufficient extension of the piston and rod structure may occur to a point where adequate stroking of the cylinder and piston cannot be accomplished under all vehicle operating conditions thereby resulting in possibly severe damage to the suspension system and other parts of the vehicle. Moreover, excessive extension of the suspension mechanism also results in over contraction or telescopic movement of the piston into the cylinder resulting in very severe fluid pressure conditions in the mechanism when hitting a rough terrain condition and thus creating higher loads on the fluid seals and the cylinder structure. The thermal loading found on prior art type liquid suspension mechanisms also contributes to degradation of the fluid seals causing leakage of fluid from the interior chambers of the mechanisms and ultimate failure of the mechanism or at least requiring frequent fluid recharging. Such characteristics are, of course, unwanted in vehicle suspension systems but have heretofore not been dealt with in a satisfactory manner.
One of the most severe vehicle suspension system applications is in relatively large off-highway trucks for hauling earth, mineral ores and various other materials and structures. Since this type of vehicle is expensive to manufacture and maintain and operates virtually at all times over very rough terrain, the provision of a spring and suspension dampening device having a suitable spring rate and being capable of complying with and dampening very severe shock loads on the vehicle is highly desired. The ability to provide a suspension spring and vibration dampener which will reduce stresses on the vehicle frame, the suspension components and tires, as well as permit increased vehicle operating speeds, can provide significant economic advantages.
Another problem associated with hydraulic cylinder and piston type vehicle suspension mechanisms, and actuators subject to similar pressures and force loadings, pertains to the provision of piston rod seals which will suitably withstand the very high hydraulic pressures and the high rates of loading and unloading, or increase and decrease, respectively, of the fluid pressures. The provision of seals which will adequately prevent leakage of fluid over a satisfactory life span of the component without scoring the piston rod and without premature seal failure has been a longstanding problem and is particularly aggravated in applications where cyclical movement of a piston rod in a cylinder at relatively high rates is encountered. In accordance with the present invention, however, improved piston rod seals are provided which are particularly adapted for applications for sealing cyclically and severely loaded mechanisms such as liquid suspension and vibration dampener mechanisms.